JPH0830777B2 - Optical fiber and method and apparatus for manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention comprises a glass fiber, a first mechanical cladding layer of synthetic rubber, and a subsequent mechanical cladding layer of synthetic resin molecularly oriented mainly in the longitudinal direction of the glass fiber. The present invention relates to an optical fiber having a synthetic resin mechanical clad portion.

The invention also relates to a method and an apparatus for manufacturing such an optical fiber.

As used herein, the term "glass fiber" shall mean a linear composite for optical transmission comprising a high refractive index glass core that may be surrounded by a low refractive index glass cladding portion. The portion may consist of one or more individual glass layers, which may or may not be chemically doped,
In addition, the glass core has a dopant concentration distribution in the radial direction thereof, so that the surrounding glass clad layer can be eliminated.

Also, as used herein, the term "optical fiber" is used to mean a glass fiber surrounded by a mechanical cladding, which is made of a durable material (eg, rubber, resin, plastic, etc.). It comprises one or more protective layers, that is, mechanical cladding layers, and has the function of protecting the incorporated glass fiber from damage, abrasion, chemical erosion and the like.

Optical telecommunications glass fibers generally have a synthetic resin mechanical cladding to prevent mechanical damage. To prevent optical transmission losses as a result of microbending, the mechanical cladding portion is preferably formed from various layers. For example, the following method is used. Immediately after forming the glass fiber, for example by drawing from a preform or by the double crucible method, a first soft buffer layer of synthetic rubber with an elastic modulus of 1 to 10 MPa is applied. A second hard top layer of synthetic resin having a modulus of elasticity greater than 100 MPa is provided to protect this soft buffer layer during subsequent processing of the optical fiber. This top layer is also applied immediately after glass fiber formation, i.e. before guiding the glass fiber onto the pulley or storing it. The buffer layer and the top layer together form the primary synthetic resin mechanical cladding of the glass fiber.

To protect optical fibers from environmental influences during cable construction, cable laying and cable life
Further, the optical fiber is provided with a thicker secondary synthetic resin mechanical clad portion having an elastic modulus of more than 1 GPa. This secondary synthetic resin mechanical clad portion is not necessarily formed immediately after the formation of the optical fiber.

Two types of shapes are used for such secondary synthetic resin mechanical cladding. In one form, an optical fiber having a primary synthetic resin mechanical cladding portion is freely located within a secondary synthetic resin mechanical cladding portion forming a tube. The space between the optical fiber and the tube is typically filled with a thixotropic liquid or gel, such as silica-filled silicone oil. Alternatively, the secondary synthetic resin mechanical cladding portion is bonded to the primary synthetic resin mechanical cladding portion by an adhesive method.

By giving some molecules of the synthetic resin mechanical cladding part a preferred orientation in the longitudinal direction of the optical fiber, it is possible to reduce the microbending loss of the optical fiber under transverse loading without causing a great temperature sensitivity. This is well known. As a result, the elastic modulus of the synthetic resin in the longitudinal direction increases, but the coefficient of thermal expansion decreases. The coefficient of thermal expansion of the glass fiber is preferably substantially equivalent to that of synthetic resin.

Electronics Letters
s) In the publication of Y. Shuto et al. in Volume 20, pp. 841-842 (1984), a method for producing such an optical fiber in which a glass fiber is clad with a buffer layer of silicon rubber is described. Has been done. There, the liquid crystalline polyester mechanical cladding is extruded at a temperature of 240 ° C. or higher to be applied to the glass fiber, and the shearing force during extrusion gives the orientation of the polyester molecules. The orientation is fixed by cooling the molten polyester and the polyester solidifies.

However, this known method presents a number of drawbacks.
As a result of the high temperatures during the extrusion process, the selection of suitable materials for the buffer layer is limited. For example, in polyurethane rubber, thermal degradation can occur during extrusion of successive layers. Furthermore, as a result of the high temperatures, long cooling paths are required and only after cooling can further processing or winding be carried out. Cooling with running water requires cooling baths over 5 meters in length, for layer thicknesses and glass fiber coating speeds that are conventional in the art. This means that if it is desired to provide the secondary mechanical cladding immediately after drawing the glass fiber,
Especially disadvantageous. Another difficulty is due to the high viscosity of the molten synthetic resin (greater than 100 Pa.s). The coating speed of glass fibers is limited by the maximum pressure that can be applied to transport the synthetic resin during extrusion. Especially when applying a thin mechanical cladding section through a narrow nozzle, pressure becomes a limiting factor.

An object of the present invention is to avoid the above-mentioned difficulties and to provide a thin mechanical grat layer of synthetic resin having an increased elastic modulus in the longitudinal direction and a coefficient of thermal expansion substantially equivalent to that of glass fiber. Providing a fiber without causing thermal degradation of the synthetic resin, and a method for efficiently producing the optical fiber at a high coating speed of a mechanical cladding layer by a shortened process and a simplified apparatus. To provide.

According to the invention, this object is formed of a synthetic resin composition in which an oriented synthetic resin is curable, said synthetic resin composition comprising one or more oligomeric compounds,
The molecule of the compound comprises a reactive group and is achieved by an optical fiber as described in the introduction characterized by a molecular weight of less than 5000.

Clad a telecommunications glass fiber with a curable synthetic resin composition immediately after formation of the glass fiber, and then curing it is described in, for example, Dutch patent application NL 8401981, Subsequent to synthetic resin, which is well known for the production of mechanical cladding, in such a case a layer of synthetic resin is formed which does not exhibit a particular orientation in the longitudinal direction of the glass fiber.

According to the invention, various choices for the position of the oriented synthetic resin mechanical cladding layer are possible. The oriented synthetic resin layer may be, for example, the top layer of the primary synthetic resin mechanical cladding portion, or it may be the closely fitted secondary synthetic mechanical cladding portion. It is also possible to manufacture both the top layer of the primary synthetic resin mechanical cladding portion and the secondary synthetic resin mechanical cladding portion from oriented synthetic resin.

As a result of polymer molecular orientation in the mechanical cladding,
High elastic modulus and low expansion coefficient of the synthetic resin in the longitudinal direction of the optical fiber can be obtained. As a result of the low viscosity of the curable synthetic resin composition, only low pressures are required for extrusion, so that high coating speeds can be achieved and also thin layers can be provided. The coating and curing of the synthetic resin composition can be carried out at low temperatures, for example below 100 ° C., so that the buffer layer of the primary synthetic resin mechanical cladding is not attacked. The coating and curing of the synthetic resin composition can in this case take place without a bath of cooling water, and can now be carried out at a very high speed, so that the cladding of glass fibers cures the secondary synthetic resin coating. If formed from a feasible synthetic resin composition, this secondary coating can be performed in one process step.

A particular advantage of the optical fiber and the method of manufacture according to the invention is that the top layer of the primary synthetic resin mechanical cladding is no longer necessary, so that the secondary synthetic resin mechanical cladding is oriented immediately after glass fiber formation. If it is provided in the form of the above-mentioned synthetic resin layer, the top layer may be omitted.

As a result of the anisotropy of the oriented synthetic resin, the water absorption of the synthetic resin mechanical cladding part results in a volume increase mainly in the radial direction of the glass fiber. As a result, this optical fiber is less sensitive to optical attenuation as a result of water absorption than an optical fiber having an isotropic synthetic resin mechanical cladding.

The curable synthetic resin composition used according to the present invention comprises reactive oligomeric molecules having a regular structure, resulting in properties similar to liquid crystal materials. The molecular weight of oligomeric compounds is less than 5000, giving the molecule sufficient flexibility to orient.

In the optical fiber of the present invention, the oligomeric compound is selected from the group consisting of polyester urethane acrylate and polyether urethane acrylate. These compounds have a very regular structure and are crystalline at room temperature in the uncured state. Curable synthetic resin compositions are further described, for example, in Dutch patent application NL 8401981/1106.
Reactive monomers as described in No. 8 and other conventional additives may be included.

According to the present invention, it is an object of the present invention to provide a method for producing an optical fiber, wherein the molecule contains a reactive group, and a curable synthetic resin composition comprising one or more oligomeric compounds having a molecular weight of less than 5000. At least 1 made of synthetic rubber
It is provided on a glass fiber having individual mechanical cladding layers, the molecules of the curable synthetic resin composition are oriented during the application of the layer to the glass fiber, and then the curable synthetic resin composition is cured and the molecules are It is mainly satisfied by a method of forming a synthetic resin oriented in the longitudinal direction of an optical fiber.

Molecules of the oligomeric compounds can be oriented during or after coating the glass fibers, for example by shear forces in a liquid. A particularly effective orientation is achieved by the method of the present invention in which the molecules of the curable synthetic resin composition are oriented by draw flow during application to the glass fiber. The drawing of the liquid is determined by the fiber drawing speed and the outflow rate of the curable synthetic resin composition, which can be adjusted by pressure, for example.

To prevent entrapment of air in the synthetic resin mechanical cladding, it is preferable to use subatmospheric pressure in the space between the glass fiber and the applied curable synthetic resin composition.

In order to fix the orientation of molecules in the curable synthetic resin composition by a crosslinking reaction, the curable synthetic resin composition must be cured within a time shorter than the relaxation time of the molecules. The relaxation time of a molecule is determined by the size of the molecule and the intermolecular attractive force. Good results are obtained with the oligomeric compounds mentioned above and with the reactive low-molecular-weight liquid crystal compounds.

Curing of the curable synthetic resin composition is performed, for example, by increasing the temperature, but in this case,
The relaxation time of oriented molecules is shorter.

In a preferred embodiment of the method of the present invention, the curable synthetic resin composition is cured by actinic radiation. Actinic radiation should be understood to mean irradiation with, for example, ultraviolet light, electron beams, X-rays, gamma rays or high-energy particles. Exposure to UV light gave cure times of less than 0.1 seconds. Particularly short curing times can be obtained by curing in a nitrogen atmosphere. Placing the irradiation device at the shortest distance from the fiber cladding forming device is effective in suppressing the alignment loss of the aligned molecules. A known advantage of using radiation curable synthetic resin compositions is that there are no solvents and other substances that must be removed from the layers formed during or as a result of curing. In the process according to the invention, this also favors the curing time and the maintenance of the molecular orientation in addition to the protection of the environment.

Another object of the present invention is to provide an apparatus for clad glass fiber with a curable synthetic resin composition, the apparatus comprising a curable synthetic resin composition for coating glass fibers. Suitable for orienting the molecules of.

According to the invention, this object is achieved by a device comprising an annular nozzle, the annulus of which the diameter is chosen to be larger than the diameter of the glass fiber (optical fiber) with which the layer is applied. It In the known glass fiber cladding forming apparatus, the glass fiber to be clad is drawn through a liquid in a container having a narrow opening for passing the glass fiber.

The present invention will be described in more detail below based on Examples and Comparative Examples and with reference to the accompanying drawings.

Example 1 Example of the optical fiber of the present invention and its manufacturing method A glass fiber is formed by a known method by drawing from a preform. The material of the glass fiber may be glass or quartz glass, in this example the material is quartz glass. The glass fiber comprises a core glass and a clad glass having different refractive indices (not shown in Figures 1a and 1b). Alternatively, a glass fiber whose refractive index changes from the center to the outside may be used.
Instead of the glass fiber drawn from the preform, a glass fiber manufactured by the double crucible method may be used. The glass fiber 1 shown in FIG. 1 has a circular cross section (diameter 125 μm), but it may instead have any other shape, for example an ellipse.

Immediately after forming the glass fiber 1, a layer of a curable synthetic resin composition is provided thereon, and then it is cured to form a buffer layer 2 of synthetic rubber having a thickness of 30 μm. The curable synthetic resin composition comprises, as described in Dutch patent application NL 8401981, a polyether urethane acrylate (76% by weight) of the following formula (I) as a main component.

The curable synthetic resin composition further comprises reactive monomers, 2
-Phenoxy-ethyl acrylate (14% by weight) and hexanediol-diacrylate (2% by weight), as well as photosensitive initiators, 2,2-dimethoxy-2-phenyl-acetophenone (2% by weight), 2,2,- Includes dimethyl-2-hydroxy-acetophenone (2% by weight) and 2-oxy-benzophenone-2-ethoxy-ethylacetophenone (2% by weight). The curable synthetic resin composition finally comprises 2% by weight of a mixture of mono- and di-2-acryloxyethyl phosphate in a molar ratio of 1: 1. Other curable synthetic resin compositions, such as polysiloxanes, are also suitable for use in the buffer layer of the synthetic resin mechanical cladding of the inventive glass fibers. The curable synthetic resin composition has an intensity of 0.27 W / cm ² measured on the synthetic resin layer for at most 0.5 seconds and is cured by irradiation from a high-pressure mercury lamp that emits ultraviolet light having a wavelength of 200 to 400 nm. The curable synthetic resin composition can also be cured by different methods, such as electron beam exposure, in which case the curable synthetic resin composition need not contain a photoinitiator.

 Then, for example, a glass fiber with a curable synthetic resin composition is used.
The second synthetic resin layer 3 is formed by clad with iva.
Provided on glass fiber with a thickness of 30 μm (see Figure 1a),
Then it is cured by exposure to UV light. Second layer (first layer
Suitable for synthetic resin mechanical cladding part top layer)
Commercially available synthetic resin compositions are sold by DeSoto Inc.
Solite 042 (DeSolite 042 ), And this one is
Do not include urethane acrylate and photosensitive initiator
It

Next, the second synthetic resin mechanical clad portion 4 is made to have a thickness of 30
It is set to 0 μm. For this purpose, a curable synthetic resin comprising 98% by weight of a polyurethane acrylate represented by the following formula (II) and further containing 2% by weight of a photosensitive initiator 1-hydroxy-1-methyl-ethylphenylketone. Use the composition.

This synthetic resin composition is applied to a glass fiber having a primary synthetic resin mechanical clad portion at a temperature of 80 ° C. The viscosity of the synthetic resin composition at 80 ° C. is 6.7 Pa.s. During application, the curable synthetic resin composition is subjected to a draw flow resulting in molecular orientation. The sequences obtained in this way are fixed by a crosslinking reaction during curing. The curable synthetic resin composition has a strength of 0.27 W / cm ² measured on the synthetic resin composition and is available from Fusion Systems.
It cures by exposure to an electrodeless mercury vapor lamp (MS Inc.). By curing in a nitrogen atmosphere and as a result of the temperature of 80 ° C., the curing time is less than 0.03 seconds.

The orientation in the formed synthetic resin layer 4 may be observable by a polarization microscope. Some measured properties of anisotropic materials are shown in Table 1.

The characteristics of anisotropic materials are low coefficient of expansion (coefficient of linear thermal expansion), high elastic modulus in the axial direction, and breaking strength. This material exhibits oriented crystals. In this example, the melting temperature of the crystal is 70
0 ° C, which indicates a low modulus at 80 ° C.
According to the present invention, it is possible to use a material having a higher melting temperature of crystals.

In another embodiment of the optical fiber of the present invention (Fig. 1b), the top layer 5 of the primary synthetic resin mechanical cladding is made of oriented synthetic resin in the manner described above, for example in thickness
40 μm. For further protection, the optical fiber may be encased in a tube 6 of thermoplastic, eg nylon, so that the glass fiber is free to move through. The result is in particular a temperature-insensitive glass fiber.

COMPARATIVE EXAMPLE A quartz glass fiber with a synthetic resin mechanical cladding is produced by the method described in the above example, but in this case curing for the formation of layer 4 (FIG. 1a) or layer 5 (FIG. 1b). Do not subject to draw flow while applying the possible synthetic resin composition. The curable synthetic resin composition is provided in the conventional manner by drawing a glass fiber through a container containing the curable synthetic resin composition. The properties of the isotropic material obtained after curing are listed in Table 2.

In contrast to Table 1, it can be seen that the properties of the isotropic material are comparable to those of the anisotropic material in the radial direction, but are significantly less suitable than the properties of the anisotropic material in the axial direction. The properties of these latter materials are just as important when used as cladding materials for optical fibers.

Embodiment 2 Embodiment of the Device of the Present Invention FIG. 2 is a schematic vertical sectional view of a device for forming a glass fiber clad of the present invention, which device comprises an upper part 10 and a lower part 11, which parts are For example, they are integrally connected by screwing. The upper part 10 has a feed conduit 12 into which a glass fiber 13, optionally already provided with a mechanical cladding layer, can be passed. Upper part 10
A space 14 is formed between the lower part 11 and the lower part 11. The curable synthetic resin composition passes through the inlet through hole 15 of the lower portion 11,
It can be applied to the glass fiber 13 via the space 14 and the annular nozzle 16. The diameter of the annular nozzle 16 is larger than the diameter of the combined glass fiber of all layers. Since the downward transfer speed of the glass fiber 13 is largely selected,
The liquid curable synthetic resin composition is subjected to stretching flow in the zone indicated by arrow 17 in the figure. In the lower part 11 there is a conduit 18 with an inlet hole 19 and an outlet hole 20 through which a heating liquid, for example water, can be passed at a temperature of 80 ° C. The upper portion 10 is provided with a through hole 21, which is connected to a vacuum pump (not shown) for forming a pressure below atmospheric pressure in the space 22 between the glass fiber 13 and the applied synthetic resin composition. can do.

[Brief description of drawings]

1a and 1b are sectional views (not drawn according to a fixed ratio) of different embodiments of the optical fiber of the present invention, and FIG. 2 is a schematic vertical sectional view of the device of the present invention. is there. 1 ... Glass fiber 2 ... Buffer layer 3,5 ... Top layer of primary mechanical cladding 4 ... Secondary mechanical cladding layer 6 ... Tube 10 ... Upper portion 11 ... Lower portion 12 …… Supply conduit 13 …… Glass fiber 14,22 …… Space 15,19 …… Inlet through hole 16 …… Annular nozzle 18 …… Conduit 20 …… Outlet through hole 21 …… Through hole

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Cornelis Marinus Herit Johem The Netherlands 5621 Beer Eindowen Früne Wautzwech 1

Claims (7)

[Claims] 1. A glass fiber, b. A first mechanical cladding layer of synthetic rubber surrounding the glass fiber, and c. A machine next to the synthetic resin surrounding the first mechanical cladding layer. An optical fiber in which the molecules of the synthetic resin are mainly oriented in the longitudinal direction of the glass fiber, the oriented synthetic resin is formed from a curable synthetic resin composition, and the synthetic resin composition An optical fiber, characterized in that the material comprises one or more oligomeric compounds, the molecules of which contain reactive groups and have a molecular weight of less than 5000. 2. The optical fiber according to claim 1, wherein the oligomeric compound is selected from the group consisting of polyester urethane acrylate and polyether urethane acrylate. 3. A glass fiber, b. A first mechanical cladding layer of synthetic rubber surrounding said glass fiber, and c. A next machine of synthetic resin surrounding said first mechanical cladding layer. In the method for producing an optical fiber in which the molecules of the synthetic resin are mainly oriented in the longitudinal direction of the glass fiber, the synthetic resin contains a reactive group and has a molecular weight of 5000 or more. A curable synthetic resin composition comprising one or more oligomeric compounds,
The synthetic resin composition is applied to a mechanical cladding layer of synthetic rubber on the outside of the glass fiber, the molecules being oriented substantially in the longitudinal direction of the optical fiber during the application of the synthetic resin composition, and subsequently, A method for producing an optical fiber, which comprises curing the synthetic resin composition. 4. The method for producing an optical fiber according to claim 3, wherein while the glass fiber is provided with the curable synthetic resin composition, the molecules of the composition are oriented by drawing flow. 5. The production of an optical fiber according to claim 4, wherein a pressure below atmospheric pressure is applied to the space between the glass fiber clad with rubber and the curable synthetic resin composition. Method. 6. The method according to claim 3, wherein the curable synthetic resin composition is cured by irradiation with actinic rays selected from ultraviolet light, electron rays, X-rays, gamma rays and other high-energy particles. Item 8. A method for manufacturing an optical fiber according to any one of items. 7. A glass which is provided concentrically with a supply conduit for vertically guiding a glass fiber surrounded by a mechanical clad layer of synthetic rubber and a space below the supply conduit and which is provided with the mechanical clad layer. A curable synthetic resin composition comprising a ring-shaped nozzle having a diameter larger than that of the fiber, wherein the molecule contains one or more oligomeric compounds having a reactive group and a molecular weight smaller than 5000. Means for pushing out from the nozzle, means for decompressing the chamber between the outlet of the supply conduit and the annular nozzle to atmospheric pressure or less, and the curable outside the mechanical cladding layer of synthetic rubber surrounding the glass fiber An apparatus for producing an optical fiber, characterized by applying a synthetic resin composition.